This proposal seeks funding for the systemic build-up and testing of retroviral vectors, which transduce anti-HIV-1 therapeutic genes into human hematopoietic cells relevant in vivo gene therapy of HIV-1 infection. In the past years, our laboratories have made significant progress in the development of two important areas in gene therapy for HIV-1 infection: (1) Dr. Pomerantz's lab has developed a series of anti- HIV-1 single chain antibodies, which significantly inhibit HIV-1 replication at early stages of the retroviral life cycle. (2) Dr. Dornburg's laboratory has developed retroviral vectors, which display single chain antibodies (scAs) or other ligands on the viral surface of spleen necrosis virus, SV. Such vectors enabled an efficient (up to 10/6 cfu/ml), cell-type- specific gene transfer into various human hematopoietic cells. Cell-type- specificity was mediated by the scA. Now, experiments will be performed to combined these two technologies to establish potent anti-HIV-1 therapeutic gene transfer systems for in vivo gene therapy for HIV-1 infection. (1) Recently, three different SNV-derived packaging systems have been developed to transduce gene specifically into various human T- cells or CD34-positive hematopoietic stem cells with efficiencies above 10/6 cfu/ml. Using these systems, vectors will be developed and systematically improved to transduce anti-HIV-1 therapeutic genes developed and tested in Dr. Pomerantz's laboratory into human T-cells. The efficiency of the gene transfer and the level of protection against HIV-1 will be determined and compared to other vector systems. (2) Cell- type specificity and the efficiency of infection of all targeting vectors will be tested in SCID mice model systems. E.G., human target and non-target cells will be implanted into SCID mice, followed by the injection of retroviral vector preparations, specific for one cell type. First, human cells as well as various mouse tissues will be investigated for the presence of marker genes transduced by the targeting vector particles. Next, the experiments will be expanded to test the therapeutic effect of anti-HIV-1 genes in vivo.